1. Field of the Invention
The present invention relates to a regenerating material for use in a refrigerator and to a refrigerator using the same.
2. Description of the Related Art
In recent years, superconductive technique has developed remarkably. The application of super-conductive technique has expanded, and the development of a miniaturized high-performance refrigerator has become proportionally important. It is demanded that a refrigerator be light and small, and have a high level of heat efficiency.
Some types of miniaturized refrigerators are known. Among them is a regeneration-type cryogenic refrigerator such as a Gifford-MacMahon (GM)-type refrigerator. A regeneration-type cryogenic refrigerator usually comprises a plurality of regenerators. Each regenerator is filled with a material having high heat-recuperation, namely, a regenerating material. The regenerating material plays an important role in exchanging heat with a coolant gas in a refrigeration cycle. Hence, the higher the recuperation property of the regenerating material, the higher the regeneration efficiency. In other words, the greater specific heat at constant volume and the higher the heat conductivity of the regenerating material, the higher the regeneration efficiency.
Hitherto used as a regenerating material in a regenerator used in a room-temperature side is copper. This is because copper has high specific heat at constant volume and good heat conductivity within a room temperature range. Lead has also been used as a regenerating material in a regenerator used in the lowest-temperature side, since it exhibits high specific heat even at low temperature. However, since the low-temperature specific heat of lead is a lattice specific heat ascribed to lattice vibration, it rapidly decreases in proportion to the cube of temperature (T) at low temperature. Consequently, the regeneration efficiency of the regenerator employing lead as a regenerating material drastically decreases at an extremely low temperature. The lowest temperature attained by the refrigerator employing such a regenerator is limited to at lowest around 10 K.
Under the aforementioned circumstances, Jpn. Pat. Appln. KOKAI Publication No. 1-310269, in which the inventors paid attention to an abnormality of a specific heat accompanying magnetic phase transition and discloses a rare earth magnetic alloy which has low magnetic transition temperature and high specific heat at constant volume at a low temperature.
However, this rare earth magnetic alloy is inevitably lacks in mechanical strengths such as abrasion resistivity and wear resistivity due to the common fragility of rare earth metals. If a refrigerator comprising regenerators charged with such a regenerating material lacking in mechanical strength is driven for a long period of time, the regenerating material becomes worn out and pulverized by the circulation of high-pressure helium gas and the like, and the fine powder generated flows out of the regenerator, damaging a helium-gas seal by adhering to a seal sliding portion. Consequently, the regeneration efficiency is significantly decreased.